CMC also referred as CMC Gum, is technically named Carboxymethyl Cellulose and is often used as a thickener and/or a texture ingredient in many applications throughout the food service industry. CMC is a man-made gum which helps products retain moisture. Gumpaste made with CMC will dry harder and be whiter in colour than those made with Gum Tragacanth.

Some in the industry also refer CMC as Tylose powder or Tylopur - which is a brand name derivative of CMC powder. This fine powder can be worked into fondant to make a really quick transition to gumpaste.
To create a quick gumpaste - knead 1-3 tsp of CMC to 1lb of a commercial fondant. In drier humidity environments use less CMC and in high humidity environments use more CMC.